When I was in middle school, my school had like 10 mangas and one of them was Ramna 1/2 and their were 2 Inu Yasha volumes. The librarian went in with a marker and blotched out the nudity and curse words.
When my sister started middle school, that was wen manga really boomed and they added a bunch of manga. The librarians did vet the comics and censor them. My sister had a copy of Full Metal Alchemist with post it note asking if the word "sex" should be blotched out. And their was one manga that they felt got a little too graphic for their liking and they ended up tearing out the pages. So their was one volume of a manga with half of the pages missing.
I found a lot of it a bit hypocritical because some of the novels in the library were far more graphic than the mangas.